High voltage electric fuse



July 22, 1958 J. c. HOWELL 2,844,691

HIGH VOLTAGE ELECTRIC Fus Filed Sept. 16, 1957 INVENTOR.

JOHN C. HOWEL BY MM ATTORNEY United States Patent 6 HIGH VOLTAGE ELECTRIC FUSE John C. Howell, Griffin, Ga., assignor to Southern States Equipment Corporation, a corporation of Georgia Application September 16, 1957, Serial No. 683,936

3 Claims. (Cl. 200-120) This invention relates to high voltage electric fuses and more particularly to corona inhibiting means for use in conjunction with high voltage fuses and cutouts.

In electric fuses and cutouts in which a fusible element is mounted within a fuse tube having a gas evolving liner, high voltage and the resulting corona discharge causes severe damage to the fusible element and to the liner. Discharge of corona produces ozone which in turn unites with the nitrogen of the air to form nitrous oxide and nitric oxide. These gases combine with water vapor to produce acids which attack the metal of the fuse link so that after a relatively short time the fuse link itself becomes corroded and its useful life and operation are thus severely impaired. Since the above described deleterious effects of corona due to high voltage are eliminated if the corona is eliminated, it has been the practice to provide various types of corona shields for use in conjunction with fuses and frequently such shields simply surround the slender fuse link and thereby render the formation of corona more diflicult due to the fact that corona is less likely to form on large diameter shields than on the relatively slender fuse link.

A principal object of this invention is to provide an improved electric fuse of the high voltage type which is constructed so that the formation of corona is virtually eliminated and which, in addition, is mechanically strong and durable.

Another object of this invention is the provision of an improved electric fuse which not only is sturdy and durable mechanically but which also incorporates desirable electrical features.

The invention in one form comprises a fuse tube constructed of glass fabric bonded into a unitary structure by means of epoxy resin and a fiber liner bonded to the inner surface of the glass fabric tube. A sleeve-like resistor made up of carbon particles is embedded within the glass fabric tube and arranged to extend from one end of the tube toward the other end but for only a portion of the length of the tube. According to a feature of the invention the terminal structure mounted on one end of the fuse tube is secured thereto by a metal pin which extends through the terminal structure and 'a portion of the tube and which contacts the sleeve-like resistor so as to form an electrical connection between the resistor and the terminal structure.

For a better understanding of the invention reference may be had to the following detailed description taken in conjunction with the accompanying drawings in which Fig. l is a side view of a conventional power fuse; Fig. 2 is an enlarged detailed view of the upper end of the structure shown in Fig. 1; Fig. 3 is an enlarged detailed view of a portion of the lower end of the fuse tube shown in Fig. 1; and in which Fig. 4 is a cross-sectional view of the fuse tube shown in Fig. 1 showing a corona inhibiting sleeve-like resistor element embedded within the glass fabric forming the main body of the fuse tube.

With reference to Fig. 1 the numeral 1 designates a metallic base on which an insulator stack 2 is mounted by means of bolts 3. Also aflixed to the channel base 1 is an insulator stack 4 which is mounted by means of bolts-5. 'Mounted to the right-hand extremity of the insulator stack 2 is the terminal structure generally designated by the numeral 6. Similarly, terminal structure generally designated by the numeral 7 is mounted on the insulator stack 4. As is well understood the circuit protected by the power fuse is connected to the terminals 6 and 7 respectively.

As is best shown in Fig. 2 the upper terminal 6 comprises a body portion 8 and a transversely disposed terminal portion 9. The terminal 6 is affixed to the insulator stack 2 by bolts 10. Affixed at pivot 11 to the body portion 8 is a sleet hood 12. Althoughnot shown in detail in the drawings the sleet hood 12 incorporates a conventional latching surface together with a biasing element which tends to impart clockwise rotation to the sleet hood 12 about the pivot 11 as viewed in Fig. 2. Such rotation of sleet hood 12 is limited by a stop element (not shown). Also mounted under the sleet hood is a contact element which is arranged to engage a contact on conducting element 13 of the terminal structure generally designated at 14 and which is mounted atop the fuse tube 21.

Terminal structure 14 comprises a body portion 15 which is secured by a pin 16 to fuse tube 21. The conducting element 13 is pivotally mounted at pin 17 to the body portion 15 and an ejector element 18 is formed on the right-hand end of conducting element 13 and a terminal screw 19 is threadedly mounted thereon. In addition to the above mentioned contact, the left-hand end of conducting element 13 is provided with a latching surface which engages the corresponding latch forming a portion of sleet hood 12. The conducting element 13 of the terminal structure 14 is maintained in the position shown in Fig. 2 by a fuse link extension 20 which is affixed by terminal screw 19 to the conducting element 13. Fuse link extension 20 extends over the prongs of ejector 18 formed integrally with conducting element 13.

From the structure described thus far and as shown 2 in Fig. 2 it will be understood that rupture of the fuse link disposed within the fuse tube 21 releases the tension of fuse link extension 20 and thereby allows the conducting element 13 of the terminal structure 14 to rotate in a counterclockwise direction about pivot 17. This rotation of conducting element 13 causes the left-hand end thereof to release the latching surface mounted within sleet hood 12 and causes the terminal structure 14 to collapse. Thereafter the fuse tube 21 and the terminal structure 14 swing in a clockwise direction about suitable trunnions affixed to the bottom of tube 21 and which engage the terminal structure 7.

As is best shown in Fig. 3 the lower terminal structure 7 constitutes a terminal portion 22 and a main supporting portion 23. Although not shown in detail in the drawing the supporting structure 23 is of conventional arrangement and constitutes a pair of spaced jaws which engage the above mentioned trunnions mounted on the terminal structure 24 which in turn is secured to the lower end of the fuse tube 15 by pin 29.

For the purpose of arresting the swinging movement of fuse tube 21 and parts associated therewith a suitable conventional snubber 25 is mounted on the terminal element 7 and cooperates with one of the trunnions forming a part of the lower terminal structure 24.

According to the invention, formation of corona is inhibited by means of a suitable sleeve-like resistor 26 shown in Fig. 4- as being imbedded within the fuse tube 21. Fuse tube 21 constitutes a tubular element 27 which preferably is formed of glass fabric bonded together to form an integral structure by means of epoxy resin. Disposed within the tubular element 27 is a fiber liner 28 3 which is securely bonded to the inner surface of tube 27 by expoxy resin or other suitable substance. As is shown in detail in Fig. 4 the fastening pin 29 not only serves to secure the terminal structure 24 to the fuse tube 21, this fastening pin 29 also serves electrically to connect the sleeve-like resistor 26 with the terminal assembly 24.

While it is desirable to locate the resistor 26 as shown in Fig. 4 and to connect it electrically with terminal structure 24 in order that the shield will be effective when the fuse is in the open position, it will be understood that the resistor 26 could be moved to the other end of tube 21 and its upper end connected by pin 16 with terminal structure 14-, if desired.

The sleeve-like resistor 26 preferably is formed of carbon particles in the form of graphite embedded within and therefore bonded to the body portion of the glass fiber by epoxy resin. According to a feature of the invention the resistance of the carbon particles should be Within the range from three meghoms per square inch to twenty meghoms per square inch. Such a resistance in accordance with conventional practice would be measured from one side of an inch square portion of the carbon layer to the opposite side thereof.

Experimental work has indicated that the structure shown in Fig. 4 and described above is mechanically strong and in addition is characterized by desirable corona inhibiting properties as well as proper electrical characteristics.

While the carbon particles are adaptable for use in desirable manufacturing techniques, the fact that carbon has a negative temperature coeflicient of resistance may result in an undesirable increase in the flow of current through the body of the tube along the resistor 26 should the temperature of the tube and of the resistor become sufficiently elevated for any reason. In view of this fact the resistor 26 is not extended along the entire length of the tube 21. Instead the resistor 26 extends only to the point designated by the letter X in Fig. 4 or to a distance of several inches from the upper end of the fuse tube 21. Thus the portion of the fuse tube between the point X and the upper end thereof which is in contact with the terminal structure 14 acts as a suitable insulator which prevents the flow of excessive current between terminals 6 and 7 through resistor 26 after the fuse link disposed within tube 21 is ruptured during a circuit interrupting operation and before terminal structure 14 disengages terminal element 6. Hence according to a feature of the invention, the resistor 26 extends from one end of the tube toward the other end of the tube but does not extend for the entire length thereof. Furthermore, according to the invention the fuse link disposed within the tube is adequately and completely protected from the deleterious effects of corona by the shield 26.

While a particular embodiment of the invention has been shown and described, the invention is not limited thereto and it is intended in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed as new is:

1. A high voltage electric fuse comprising a hollow fuse tube constructed of glass fabric bonded together with epoxy resin, a fiber liner bonded to the inner surface of said tube, a sleeve-like resistor formed of carbon particles embedded within and bonded to said glass fabric with said epoxy resin and extending from adjacent one end of said tube toward the other end thereof for a portion only of the length of said tube, the resistance of said resistor being in the range of three to twenty megohms per square inch, terminal structure mounted on said one end of said tube, and a fastening pin extending through said terminal structure and through the wall of said tube and engaging said resistor to secure said terminal structure in position on said tube and to form an electrical connection between said resistor and said terminal structure.

2. A high voltage electric fuse comprising a hollow fuse tube constructed of glass fabric bonded together with epoxy resin, a fiber liner bonded to the inner surface ofv said tube, a sleeve-like resistor formed of carbon particles embedded within and bonded to said glass fabric with said epoxy resin and extending from adjacent one end of said tube toward the other end thereof, terminal structure mounted on said one end of said tube, and fastening means for securing said structure to said tube and for forming an electrical connection between said structure and said resistor.

3. A high voltage electric fuse comprising a hollow fuse tube constructed of glass fabric bonded together with epoxy resin, a fiber liner bonded to the inner surface of said tube, a sleeve-like resistor formed of carbon particles embedded within and bonded to said glass fabric with said epoxy resin and extending from adjacent one end of said tube toward the other end thereof, and terminal structure mounted on said one end of said tube and electrically connected with said resistor.

References Cited in the file of this patent UNITED STATES PATENTS 1,730,716 Austin Oct. 8, 1929 2,528,932 Wiles et al. Nov. 7, 1950 2,567,768 Fahnoe Sept. 11, 1951 2,593,426 Fahnoe Apr. 22, 1952 2,727,961 Smith Dec. 20, 1955 

